Predictions are presented for a selected compressor using longer hole-pattern seals with L/D ratios from 0.5 to 2.5. Results were obtained for back-to-back and in-line compressors with the seal located at mid-span and at 82% of rotor span respectively, considering different seal lengths, radial seal clearances, as well as constant clearance and convergent-tapered seal geometries. Predictions of the synchronous rotordynamic coefficients and leakage were estimated using a code developed by Kleynhans and Childs with zero preswirl and constant pressure ratio of 0.5. This code does not include moment coefficients; which can affect the results. Results of all configurations show an increase of stiffness and damping coefficients with increasing seal length. In addition, a significant reduction in leakage (approximately 47 percent) as L/D increases is exhibited for constant clearance and convergent-tapered hole-pattern seals. For the back-to-back compressor, the stability analysis predicts that the system is stable for all speeds and L/D ratios. In fact, the rotor cylindrical-bending mode becomes more stable with lengthening the seals, for both constant clearance and convergent-tapered hole-pattern seals. For constant clearance seals (Case A), the synchronous response at mid-span show a critical speed at 8,000 rpm (cylindrical-bending mode) for all L/D ratios, while a reduction of 85 percent in the peak response is exhibited as L/D increases. Case B, in which the radial clearance is increased as L/D increases to have the same leakage as case A, slightly increases the synchronous response of the model compared to case A. For convergent-tapered seals (Case C), the synchronous response at mid-span shows a higher critical speed (9,000 rpm) for all L/D ratios, and a larger reduction (89 percent) in peak response with increasing L/D, compared to Case A. However, the magnitude of the peak response is larger for convergent-tapered seals than that for constant clearance seals, for all L/D ratios. For in-line compressor, the stability analysis predicts two critical speeds at 6,000 (conical mode) and 18,000 rpm (first bending mode) respectively. Both modes are predicted to be stable for all speed and L/D ratios. Synchronous response at the mid-span for Case A shows the peak response at the first critical speed is slightly reduced as L/D increases while the response at the second critical speed is increased for most of the cases. In addition, the second critical speed is reduced from 18,000 to 13,000 rpm, which is not a concern because it remains above the running speed. This was also the trend for convergent-tapered hole-pattern seal. In addition, the increase of radial clearance in Case B slightly increases the amplitude of vibration, compared to Case A.

The electroreflectance spectra(ER) have been measured on InxGa1-xAs film under various bias(Vbias), and they have exhibited many Franz-Keldysh Oscillations(FKOs) above band-gap energy. Their strength of field in the film can be obtained by the periods of FKOs. Due to many oscillations of FKOs, the Fast Fourier transform can be applied to separate heavy- and light-hole transitions. The relation between F and Vbias was nearly linear. FKOs were observable at a large range of photon energy(£_E). The mean free path of carriers can be estimated from the relation between £_E and F. It was compared with the range of order obtained from X-ray diffraction.

This thesis documents the results of high pressure testing of hole-pattern annular gas seals conducted at the Texas A&M University's Turbomachinery Laboratory. The testing conditions were aimed at determining the test seals sensitivity to pressure ratio, inlet fluid preswirl, rotor speed, and rotor to seal clearance. The rotordynamic coefficients showed only small changes resulting from the different pressure ratios tested. Only the damping terms at the lower frequencies showed some influence. One other notable result from the testing of different pressure ratios is that the seals were tested in a choked flow condition, and there was not a significant change in the seal behavior when the seals transitioned to the choked condition. The inlet fluid preswirl only had a notable effect on the cross-coupled stiffness in the larger clearance tests. These results lead to the conclusion that a swirl brake could have some rotordynamic value, but only if the seals have sufficiently large clearance. Conversely this also means that if hole-pattern seals are being implemented with a small clearance, then a swirl brake would not be an effective way to improve the rotordynamic stability of the system. The only significant effect that the rotor speeds had on the rotordynamic coefficients were that the cross-coupled coefficients increased as the rotor speed increased. This is the expected result because as the rotor speed increases there is a greater shear force on the gas as it passes through the seal resulting in more fluid circumferential velocity, which results in stronger cross-coupled coefficients. The changes in clearance resulted in drastic changes in the magnitude of the coefficients. The smaller clearance yielded much higher coefficients than the larger clearance. All of the rotordynamic coefficients were predicted well by ISOTSEAL. The code was found to do a good job predicting the seal leakage as well. This gives more credence to the coefficients and leakage that ISOTSEAL predicts.

No description available.

In recent work by Kraus and Wilczek, it is first uncovered that small deviations from exact thermality in Hawking radiation have the capacity to carry off the maximum information content of a black hole. It is summarized, simplified and extended in this dissertation. This goes a considerable way toward resolving a long-standing “information loss paradox.” / Graduate

The magmatic processes involved in building the plutonic section of the oceanic crust at fast-spreading centers remain debated. At this stage, no intact section of this important lithospheric layer, known as seismic layer 3, has been drilled. Yet, Ocean Drilling Program Hole 1256D, located on the eastern flank of the East Pacific Rise, provides unparalleled opportunities to investigate the mode of emplacement and fabric development of the two uppermost gabbro bodies in this crust. Although inferences made from a drill core remain limited due to the intrinsically linear nature of observations, the samples recently recovered hold potential clues on fabric-forming processes and the magma convection in such small intrusions. Gabbro 1 forms a 52 m-thick body intruded in the texturally granoblastic altered zone of the sheeted dike complex. Gabbro 2, situated below gabbro 1, is only 24 m-thick. Both gabbro bodies lack a macroscopically visible fabric and were, until this study, considered structurally isotropic. We use digital image analysis of petrographic thin-sections and the intercept method (Launeau and Robin, 1996) to determine the shape-preferred orientation of plagioclase phenocrysts in 3-D. Thirty-three sets of three mutually perpendicular thin-sections were prepared and analyzed in this manner. The mode of plagioclase grains ranges from 15 to 20% in the upper interval of gabbro 1, 13 to 36% in the lower interval of gabbro 1, and 9 to 28% in gabbro 2. These values refer to the mode of euhedral to subhedral grains only and do not reflect the total mode of plagioclase in the rock. The two gabbros display a weakly anisotropic shape-preferred orientation characterized by an average shape ratio > 1.050. The aspect ratio indicates plagioclase fabric strength deviation from a perfectly anisotropic distributed population. The aspect ratio in the upper interval of gabbro 1 ranges from 1.068 to 1.153. The aspect ratio in the lower interval of gabbro 1 ranges from 1.074 to 1.183. The aspect ratio in gabbro 2 ranges from 1.056 to 1.220. The fabric of these gabbros also displays broad consistency between nearby specimens. Lineation plunges in the upper interval of Gabbro 1 range from 1° to 36°. Lineations plunge in the lower interval of gabbro 1 range from 0° to 44°. Lineations in gabbro 2 plunge from 6° to 69°. In general, the symmetry of plutonic fabrics provides clues on the nature of magmatic fabric-forming processes. Prolate fabrics support magmatic flow while oblate fabrics rather suggest gravitational settling of crystals. Fabrics in gabbro 1 and gabbro 2 are both prolate and oblate. Fabric in the upper interval of gabbro 1 is more prolate than oblate whereas the lower interval of gabbro 1 and gabbro 2 have even distributions of fabric ellipsoids. Detailed observations of petrographic thin-sections reveal several microstructures suggestive of brittle and plastic deformation in plagioclase grains. Microstructures indicative of plastic deformation include kink-banding, mechanical twinning, and undulose extinction. Microstructures indicative of brittle deformation include submagmatically-fractured laths. These subtle features appear in at least one crystal per thin-section analyzed. With the exception of mechanical twins, shipboard scientists of Expeditions 312 and 335 have not documented these microstructures. Numerical calculations reveal that for both gabbro bodies the Rayleigh Number ranges between 1015 and 1018, depending primarily on the kinematic viscosity of the magmas and temperature change across the intrusions. These values indicate that turbulent flow (Rayleigh number > 106) occurred during emplacement. This type of flow may provide an explanation for the variability of aspect ratio and the variability in linear crystal fabric.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998. / Includes bibliographical references (leaves 93-97). / by Mary Ann Schlegal. / M.S.

No description available.

No description available.

No description available.